‘They are changing their behaviour and becoming more savvy shoppers when it comes to groceries, but there’s only so much they can do to cut back on the basics.’

Researchers Mintel said ‘brand loyalty is typically the first casualty’, adding: ‘Despite a heavyweight promotional culture in the UK, three quarters of consumers are more concerned about rising food prices than they were a year ago.

‘And the situation is about to worsen amid warnings of higher prices to come.’

The volume of food and grocery sales is down by 1.7 per cent compared with a year ago, according to retail analyst Nielsen.

Mike Watkins, its senior manager for retailer services, said: ‘Inflation is dampening demand and retailers are seeing falling unit sales as shoppers continue to struggle not only with food costs but with rising fuel prices and utility bills as well.’

Supermarket dash: Some aisles we used to linger in will be ignored as prices rise

The annual rate of price increase for all types of food hit 4.9 per cent in May, driven by a surge in the cost of commodity crops such as wheat and corn. Wheat prices are up by 72 per cent in a year, pushing up the cost of supermarket own-label pasta and baguettes.

Droughts in many parts of Europe – including the UK – have exacerbated the problem by hitting yields of many food crops, says the British Retail Consortium.

And as bills rise, Asda’s monthly income tracker claims families were an average of £9 a week (or 5.1 per cent) worse off in June 2011 than they were a year ago.

This fall in spending power has been running for four years, making it the most prolonged squeeze on living standards since the 1870s, according to some analysts.